Modern vehicle concepts and structural designs of vehicles have a plurality of cavities which have to be sealed in order to prevent the ingress of moisture and contaminants, since the latter can result in corrosion from the inside on the corresponding body parts. This applies, in particular, to modern self-supporting body constructions in which a heavy frame construction is replaced by so-called “space frames”. With the latter, use is made of a lightweight, structurally solid chassis made of prefabricated hollow sections. Such constructions have, depending upon the specific system, a number of cavities which have to be sealed against the penetration of moisture and contaminants. These cavities include the upwardly extending A-, B- and C-pillars supporting the roof structure, the roof rail, portions of the fenders, or the sill. In addition, these cavities transmit airborne sound in the form of unpleasant vehicle running noises and wind noises. Therefore, such sealing measures also serve to reduce the noises and to enhance the comfort of traveling in the vehicle.
During the assembly of the car, these frame parts and body parts containing cavities are prefabricated from half-shell components which were joined at a later time by welding and/or adhesive bonding so as to form the closed hollow section. Within this specification, such half-shell components after joining are called “interconnected walls”, which surround the enclosed hollow section (“cavity”). With such a type of construction the cavity in the early body in white (“body shop”) state of a vehicle body is accordingly easily accessible, so that sealing and acoustically damping baffle parts (sometimes referred to as “pillar fillers” or “cavity filler inserts”) can be fixed in this early phase of body construction by mechanical hanging, by insertion into appropriate holding devices, bores or by gluing or welding to the cavity walls.
Most modern baffles or pillar fillers are designed to include a sealing material disposed on a support member or carrier. The carrier is generally manufactured from a rigid material, such as hard plastic, such that its shape approximates the shape of the cavity to be sealed. The carrier/sealing material combination is configured such that the carrier is inserted into a cavity. Typically, the sealing material is activated (thermally or chemically) to expand (or “foam”) after insertion into the cavity so that the sealing material forms a seal with the walls of the cavity. Thus, the expanded sealing material creates an airtight seal between the carrier and the walls of the cavity.
WO 00/03894 A1 discloses a lightweight expandable baffle for sealing a cavity of a vehicle body at a predetermined cross section of the cavity. This baffle includes a rigid support plate having an outer periphery with a shape generally corresponding to but smaller than the shape of the cross section of the cavity. Said baffle comprises a heat expandable sealing material mounted to the outer periphery of the rigid support plate having an activation temperature range at which the material expands. The support plate is being formed of a material having a higher melting point than the activation temperature range of the sealing material. When activated, the sealing material expands radially from the rigid support plate to fill the cross-sectional cavity between the rigid support plate and the cavity walls.
WO 01/83206 A1 discloses a combined baffle and reinforcing assembly for use within the cavity of a structural member to dampen acoustic transmissions through the cavity and to provide reinforcement in a direction transverse to the longitudinal axis of the structural member. The combined assembly includes a synthetic carrier which comprises an interior area, a marginal rim and an attachment member preferably in a form of a clip suited for insertion to the corresponding hole in the wall of the structural member. The carrier is circumscribed by a continuous band of reinforcing material extending around the periphery of the carrier. The marginal rim of the carrier may include a base wall and a support flange for receiving the thermally expandable material thereon.
According to the state of the art, the carrier usually is shaped as a plate. This plate may be formed from metal or from thermoplastics, in which case the thermoplastics may optionally be fiber-reinforced. Preferred thermoplastics are polyamides, polyimides, polyoxypropylene or polyethylene terephthalate. The thermoplast has a melting point higher than the expansion temperature of the heat expandable material. The carrier plate, optionally including the support structure, is preferably made by injection molding. In preferred embodiments, the thermoplastic carrier plate and the heat expandable material are either formed in one co-extrusion process or in subsequent extrusion processes on the same injection molding unit.
In the pillar filler design of the state of the art, the carrier plate acts as a barrier which mainly ensures the sealing of the cavity and which contributes moderately to the acoustic damping properties of the complete baffle. The present invention solves the problem of increasing the acoustic damping efficiency of pillar fillers comprising a thermally inert (at the temperatures to which the pillar filler is exposed) carrier made of a thermoplastic material, and a thermally expandable (“foamable”) material which, after foaming, fills the space between the carrier and the inner walls of the cavity.